The present invention relates to a clutch disc suitable for vehicles and has as its objects to increase a maximum torsion angle and to facilitate various intended changes of torsion characteristic by modifying the shape and size of a few parts or members.
Attempts have been made to increase the maximum torsion angle of clutch discs to increase in order to lower vehicle noise. More concretely, in a graph of load-torsion angle characteristic line in which a vertical axis is load and a horizontal axis is torsion angle, incline of the characteristic line is required to be small while the angle increases from zero (0) to a predetermined large value. In other words, an increasing rate of the load should be small with respect to a increasing rate of the angle. Then, in torsion angle area over said predetermined value, the increasing rate is required to increase once or twice like a bent line. Therefore, in the conventional construction, a hub flange, a clutch plate and a retaining plate should have circumferentially long openings in which torsion springs are engaged. However, length of the openings have already increased to approximately maximum limit with respect to torque capacity and space allowed in the disc.